Product responsive relay with a variable-q filter



Nov. 3, 1970 J. M. CROCKETT PRODUCT RESPONSIVE RELAY WITH A VARIABLE, -QFILTER mmOE m OE w 1 ZU UKQ h NW Pr flumZO 7 0G .P m Owmm m W 4 M 5 v Am m J u r m a N 8 Filed Aug ATTORNEY Nov. 3, 1970 J. M. CROCK ETT3,533,334

PRODUCT RESPONSIVE RELAY WITH A VARIABLE -Q FILTER Filed Aug. 28, 1967 I3 sheets-sheet 2 n n n m nnr U U 5 CIRCUIT BREAKER Nov. 3, 1970 J. M.cRockETT 4 PRODUCT RESPONSIVE RELAY WITH A VARIABLE Q-F ILTER Filed Au28,1967 I s Sheets-Sheet s CIRCUIT BREAKER 52"" FIG. 30.

' MAXIMUM CURRENT vEci'oR MAXIMUM HFOR'MAXIMUM' TORQUE TORQUE 9 onoue Aa c V F IG.4.

r 3:: as 37 United States Patent Office 3,538,384 Patented Nov. 3, 1970U.S. Cl. 317-27 4 Claims ABSTRACT OF THE DISCLOSURE This disclosurerelates to a line protecting relay network which is energized throughtwo input circuits each of which resonate at the line frequency. A ringmodulator is provided to render the output sensitive to the phasedifference of the signals applied to the two input circuits. The twoinput signals may be energized by two quantities derived from the lineto be protected and the net result used to control the operations of acontrol circuit of a circuit breaker.

Applicant hereby claims the benefit of the priority of his copendingCanadian application Ser. No. 973,810 filed Oct. 22, 1966, for ProductResponsive Relay.

This invention relates to relays and in particular to relays which areresponsive to the product of two quantities.

Under various conditions it is advantageous to utilize a relay which isresponsive not only to a single quantity but in fact to the algebraicresult of the multiplication of two quantities, including their phaseangle. Relays of this type have a particular application in grounddetection and distance relaying. Variousrelays of this type have beenproposed in the ,past including induction disc and induction loop orcylinder relays. With the increase in speed of operation of variouselements in power systems, it has been necessary to increase the speedof operation of relays. The trend therefore recently has been toward theutilization of semiconductor devices tocombine various signals and theultimately control the contacts of a device such as a circuit breaker.

, When such semiconductor devices are used in the control circuitryandthe circuitry is arranged for rapid response there is always thedanger that the relay may respond to transients which do not representan actual condition to be sensed. Elimination of such transients bymeans of filters, however, may give riseto time delays whicharecharacteristic of filters which may or may not be objectionable underthe circumstances.

Since most power systems are three phase, it is also desirable that thesignal should be applicable from all three phases to as much of thecommon circuitry as possible in order to eliminate redundancy andmultiplicity of apparatus.

In accordance with the present invention, the foregoing problems of theprior art are overcome by providing resonant circuits in the input whichresonate at the frequency of the power system, thus substantiallyeliminating transients. At the same time the filters used in the relaymay be switched so that they are only operative during the period when afault may occur. In this way the time delays introduced by the filterare minimized. The quantities to be combined are applied to a ringmodulator otherwise known as a diode phase comparator Which combines thetwo input signals and produces an output depending upon the amplitudeand phase angle of the inputs. Theoutput from the phase comparator isapplied to a semiconducting circuit which evaluates the product of theinput signals for each half cycle and controls a contacting type outputrelay and/or a semiconductor voltage output circuit to produce outputswhich may be used in various ways to control the power system.

A clearer understanding of my invention may be had from the followingdescription and drawings, in which:

FIG. 1 is a schematic diagram of a relay in accordance with myinvention.

FIG. 2 is a series of waveform diagrams useful in explaining theoperation of such a relay.

FIG. 3A is a power system arranged to provide the necessary signals tothe relay for detecting ground faults as a ground directional relay withzero sequence current compensation.

FIG. 3B similarly is arranged to provide the necessary signals to therelay to permit it to operate as a dualpolarized ground directionalrelay.

FIG. 3C shows a power system arranged to supply the necessary signals tothe relay to operate the relay as a current polarized relay.

FIG. 3D shows a power system arranged to provide the necessary signalsto permit operation of the relay as a directional relay.

FIG. 4 is a series of relay characteristics arranged to illustrate threepossible modes of operation of the relay as a ground directional relay.

FIG. 5 is one possible arrangement of the switch filter circuit.

FIG. 6 is a further possible arrangement of a switch filter circuit, and

FIG. 7 is a series of RX diagrams representing three possiblecharacteristics of the relay operating as a distance relay.

Considering first FIG. 1, it will be seen that one input terminaldesignated 1 is connected through resistor 2, transformer primary 3, thesecondary of mutual reactor 4, and capacitor 5 to terminal D. Diodes 6,7, 8 and 9' are arranged as a ring modulator. One end of the centretapped secondary of transformer 3 is connected to the junction of diodes6 and 7 and the other to the junction of diodes 8 and 9. Terminals C andD are connected to the primary of mutual reactor 12 and the secondary ofthis reactor 12 is connected at one end to centre tap of the secondaryof transformer 3 and at the other end through capacitor 13 to anadjustable point on a potentiometer consisting of resistors 14, 15 and16 in series between the junctions of diodes 6 and 8 and 7 and 9. Theoutput from this phase comparator is applied through resistor 17 betweenthe base and emitter of transistor 18. The collector of transistor 18 isconnected to the positive supply line 19 through resistor 20 and theemitter of transistor 18 is connected to the negative supply line 21.The collector of transistor 18 is also connected through the resistor 22to the base of transistor 23. The collector of transistor 23 isconnected through resistor 24 to the positive supply line 19. Theemitter of transistor 23 is connected through resistor 25 to thenegative supply line 21. The emitter of transistor 23 is also directlyconnected to the base of transistor 26. The collector of transistor 26is connected through resistor 27 and variable resistor 28 to thepositive supply line 19. The emitter of transistor 26 is connected tothe negative supply line through diode 29. The collector of transistor26 is also connected through resistor 30 to capacitor 31; the otherterminal of this capacitor being connected to the negative supply line21. The collector of transistor 26 is also connected through Shockleydiode 32 and resistor 33 and resistor 34 to the negative supply line 21.The junction of resistors 33 and 34 is connected through diode 35 andcapacitor 36. to the negative supply line 21. The

junction of diode 35 and capacitor 36 is connected through resistors 37and 38 to the negative supply line. The junction of resistors 37 and 38is connected to the base of transistor 39. The emitter of transistor 39is connected to the negative supply line 21, and the collector isconnected through the coil of relay 40 to the positive supply line 19.

Diode 41 is connected across the coil of relay 40. The contacts of relay40 consists of a single pole double throw switch of the type referred toas make before break. The stationary contacts of this relay areconnected together through a protective circuit comprising resistor 42and capacitor 43.

Capacitor 44 is connected across diode 32 and resistor 33 and thejunction of this capacitor and resistor 33- is connected through diode45 to the negative supply line through capacitor 46. The junction ofdiode 45 and capacitor 46 is connected to the negative supply linethrough resistors 47 and 48. The junction of resistors 47 and 48 isconnected to the base of transistor 49. The emitter of transistor 49 isconnected to the negative supply line 21 and a collector is connectedthrough resistor 50 to the positive supply line 19. The collector isalso connected through resistor 51 to the base of transistor 52. Theemitter of transistor 52 is connected to ground and the collector isconnected through resistor 53 to the positive supply line 19. Thecollector of transistor 52 is connected to the output terminal 54 whichterminal is also connected to the negative supply line through Zenerdiode 55.

Supply for the semiconductor circuitry is provided from the positive andnegative terminals 56 and 57 respectively, terminal 57 being connecteddirectly to the negative supply line and terminal 56 being connectedthrough resistor 58 to the positive supply line 19. Zener diode 59 andprotective diode 60 and capacitor 61 are all connected between thepositive supply line 19 and the negative supply line 21.

OPERATION The inductance provided by the primary winding of thetransformer 3 and the secondary winding of the mutual reactor 4 togetherwith the capacitance of capacitor form a resonant circuit resonant at 60cycles or the normal frequency of supply. In a similar manner theinductance provided by the secondary winding of the reactor 12 togetherwith the capacity of capacitor 13 form a series resonant circuitresonant at 60 cycles. Because both of these circuits are resonant atthe supply frequency they are relatively immune to spurious responsesdue to transients. Since the elements between terminals 1 and 0represent a series resonant circuit the currents between terminals 1 and0 will be a maximum at resonance and therefore the output from thesecondary of transformer 3 will be a maximum at the resonant frequencyof the series circuit. Similarly the current provided by the secondaryof transformer mutual reactor 12 will be a maximum at its resonantfrequency.

As has been previously indicated, diodes 6, 7, 8 and 9 are arranged as aring modulator or phase detector and arranged so that when the two inputcurrents applied by the secondary of transformer 3 and that applied bythe secondary of mutual reactor 12 are of the same instantaneouspolarity, the junction point of diodes 6 and 8 becomes positive withrespect to the junction point of diodes 7 and 9, thus applying apositive potential through resistor 17 to the base of transistor 18 andcausing transistor 18 to be turned on. On the other hand, when the twoinput currents are not of the same instantaneous polarity or if eitherinput is zero the output voltage will be negative or zero and transistor18 will be turned off.

With transistor 18 turned on, its collector is effectively connected tothe negative supply line thus switching olf transistor 23 which in turnswitches off transistor 26. With transistor 26 switched off itscollector is essentially 4 at the positive supply line potential, exceptfor any resistance drop through resistors 27 and 28, and the capaci tor31 charges through resistor 28, resistor 27 and resistor 30. If theresulting potential at the collector of transistor 26 reaches a setvalue the diode 32, which is a Shockley diode, breaks down and thecharge stored in capacitor 31 is transferred through resistor 33, anddiode 35 to capacitor 36 and also through resistor 33 and diode 45 tocapacitor 46. Since the potential which determines breakdown is thepotential across the Shockley diode 32 it is necessary to thesatisfactory operation of the circuit that the potential across theShockley diode be the potential at the collector of transistor 26 withreference to ground. Diodes 35 and 45 create the necessary isolationbetween the subsequent circuit and the Shockley diode, so thatpotentials on capacitors 36 and 46 cannot appear at the junction ofresistor 33 and 34.

When capacitor 36 is charged, it raises the potential applied to thepotentiometer consisting of resistors 37 and 38 thus raising the base oftransistor 39 to a positive potential causing this transistor to switchon and a current to flow through the control winding of relay 40.

In a similar manner the potential on capacitor 46 is applied to thepotentiometer consisting of resistors 47 and 48 causing the base oftransistor 49 to become positive thus switching on this transistor. Whenthe transistor 49 becomes conductive its collector is effectivelyconnected to the negative supply line causing the base of transistor 52to be negative thus switching off transistor 52 and raising thepotential of its collector to the positive supply line potential andproducing a positive potential on terminal 54. An output can be derivedfrom the circuit either from the contacts of relay 40 or from theterminal 54 depending upon the subsequent apparatus to be controlled. Asshown in the diagram, the relay 40 is deenergized, the normally opencontacts are open and this de-encrgizes the trip circuit for the circuitbreaker.

There are two adjustments in the circuit for determining its point ofoperation, the first adjustment is on the adjustable resistor 15 whichis set up to provide the proper balance of the phase detector circuit toensure that under zero input conditions there is zero output. With acurrent provided from the secondary of mutual reactor 12 and no inputprovided from the secondary transformer 3, for example, there should beno output across the terminals of the ring modulator.

The second adjustment has to do with the charging of capacitor 31. Itwill be noted that the charging circuit of this capacitor includesresistor 28 which is adjustable. Since the Shockley diode breaks downwhen capacitor 31 reaches a particular potential, it will be seen thatthe operation of the relay is dependent upon the length of time requiredfor capacitor 31 to arrive at a particular potential. By adjustment ofresistor 28 the rate of charge of capacitor 31 can be adjusted. At thesame time, in order to avoid improper operation when a series ofbreakdowns of the Shockley diode occur causing charging of capacitor 36and 46, it is necessary to ensure that the Shockley diode 32 continuesto operate based upon the potential between the collector of transistor26 and ground. As was previously indicated, diodes 35 and 45 perform thefunction of isolatingcapacitors 36 and. 46 from the Shockley diode.Resistor 34.connects the junction of the diodes 35 and 45 and resistor33 to ground, the resistance of resistor 34 is much less than the backresistance of the diodes 35 and 45; therefore this point effectivelyconnected to ground and the potential effective across the Shockleydiode 32 is the potential between the collector of transistor 26 andground. By adjustment of resistor 28 therefore, the characteristic ofthe relay may be adjusted, determining the length of time transistor 18must be switchedon before the relayoperates and this in turn determiningthe necessaryphase angle difference between the currents supplied to thering modulator from the two different sources in Order to produce relayoperation.

Considering now FIG. 2, there is shown at a a graph of voltage versustime of the power system. This graph will be used as a reference for theremaining waveforms illustrated. Waveform 11 illustrates a currentwaveform in phase with the voltage waveform shown at a which might occurin one of the phases or in the groundreturn of the current transformersand be used to provide one of the inputs to thering modulator. Assumingthat the waveform shown at a is used as the primary input to themodulator, waveform c is a further current waveform which might be usedas the second input to the ring modulator having a phase difference of90 with respect to waveform a. This waveform might be provided to thering modulator under various circumstances. Waveform d is a yet furthercurrent waveform which might be applied to the ring modulator underother circumstances where the current is 180 out of phase with thereference voltage shown at a. Waveform e shows the output voltage fromthe ring modulator which is applied to the base of transistor 18 whenthe input waveforms are as shown at a and b. It will be noted that thering modulator produces a substantially constant output until one orboth of the waveforms approach zero, this results in a substantiallyconstant output voltage with spikes projecting down to the zero line.Waveform 1 shows the output from the ring modulator when waveforms asshown at a and c are applied as an input. It will be noted that asubstantially constant output pulse is produced while waveforms a and care either both in the negative direction or both in the positivedirection and that a substantially constant negative going pulse isproduced when the waveform at a is in a positive direction and theWaveform at c is in the negative direction or conversely when thewaveform at c is in the positive direction and the waveform at a is inthe negative direction. The waveform at g represents the output from thering modulator when waveforms a and d are used as inputs to the ringmodulator and it will be noted it consists of a series of negative goingpulses of substantially constant amplitude with intervening spikes goingup to the zero line where one or both of the waveforms approaches zero.

. Since transistor 18 becomes conductive only when the appliedwaveformgoes in a positive direction the output from transistor 18 will besimilar to the waveform shown at e, f and g, except that it will beclipped and not have any excursions in the negative direction. As aresult, waveform g ceases to exist, in effect, since no values below thezero line are reproduced in the output of transistor 18 and the waveformf is clipped at the zero line. The waveform at h shows the potential atthe collector of transistor 26 when the waveform e is applied to thebase of transistor 18. As soon as transistor 18 is turned on, transistor26 is turned off, and capacitor 31 begins charging through resistors 28,27 and 30. As was previously indicated the rate of charge is determinedby the setting of variable resistor 28. The capacitor starts to chargebut before it reaches the reference line r the waveform goes to zero,transistor 18 switches off, transistor 26 switches on and the capacitoris discharged down to the zero line. In the next cycle, the capacitorbegins to charge when transistor 26 is switched off and rises until thevoltage on the collector of transistor 26 reaches the reference line rat which point Shockley diode 32 begins conducting and a portion of thecharge on capacitor 31 is transferred through resistor 30, resistor 33,diode 35 to capacitor 36 thus reducing the voltage on capacitor 31.Transistor 26, however, remains cut off and the charging continues upthe second charging curve until transistor 18 is once more switched off,transistor 26 is switched on and the capacitor 31 is discharged.

The next waveform shown at h indicates what occurs when resistor 28 isreduced in value. Referring to the Waveform that starts at point M atwaveform h it will be seen that the slope of the curve is much steaperbecause resistor 28 is less. The reference line is therefore reachedearlier in time. Shockley diode 32 breaks down and capacitors 31 and 36start to recharge, after the voltage is first reduced due to thetransfer of charge from capacitor 31 to 36. The voltage at the collectorof 26 once more rises to the reference line and it will be noted thatbecause of the presence of the isolating diode 35, the potential acrossthe Shockley diode 32 is, as was previously indicated, effectively thepotential between the collector of transistor 26 and ground. TheShockley diode therefore once again breaks down and further charge istransferred from capacitor 31 to capacitor 36. Capacitor 31 then onceagain begins to recharge until either transistor 26 becomes conductiveor the Shockley diode breaks down whichever occurs first.

As illustrated, it is assumed that the transistor 26 once more becomesconductive because the waveform e has once more gone to zero, thiscauses the capacitor 31 to be completely discharged and the cycle beginsover again. If resistor 28 is decreased still further then the rate ofcharging of capacitor 31 increases as shown in the latter two waveformsillustrated at h. The operation does not differ from that previouslydescribed except, that the rate of charging being of greater, thevoltage arrives at the reference level r in a lesser time causing agreater series of breakdowns of the Shockley diode and transfers ofenergy from capacitor 31 to capacitor 36. It should be understood whenreference is made to transfer of enrgy from capacitor 31 to capacitor 36there is simultaneously occurring a transfer of energy from capacitor 31to capacitor 46 through resistor 33 and diode 45.

Considering now waveform i of FIG. 2, this waveform is the waveform ofthe voltage at the collector of transistor 26 when the waveform f isapplied to the base of transistor 18, It will be seen that nothingoccurs until the waveform at 1 goes positive causing transistor 18 tobecome conductive and transistor 26 cut off. At this point the capacitor31 begins to charge and let us assume that it charges at the same rateas it did in waveform h, that is, resistor 28 has been set to the sameposition as it was in the first three waveforms of waveform h. It willbe seen, that the potential at the collector of transistor 26 neverreaches the breakdown potential of the Shockley diode 32 and thecapacitor therefore goes on charging until transistor 26 becomesconductive causing it to discharge at the end of the positive waveformf. Capacitor 31 remains discharged until waveform once more goes apositive at which point it once more begins to charge but again does notever reach the breakdown potential of the Shockley diode and no furthereffect occurs. At the next waveform, however, it has been assumed thatthe resistor 28 has been reduced in value as it was with reference towaveform h. It will be noticed now that the rate of charge of capacitor31 increases and the potential at the collector of transistor 26 risesat a greater rate and reaches the reference line r at which point theShockley diode 32 breaks down causing a transfer of energy to capacitor36 through resistor 33 and diode 35. Capacitor 31 now begins to rechargeand before it reaches the reference line r, transistor 18 becomesnon-conductive because the wave form 1 assumes a negative polarity,transistor 26 becomes conductive and capacitor 31 is discharged. Thiscycle is once more repeated when the waveform f assumes a positivepotential. When, as shown in the latter waveforms of waveform h, theresistor is reduced still farther capacitor 31 charges at a greaterrate, the potential rises more rapidly until it reaches the referenceline 1' at which point the Shockley diode 32 breaks down permittingtransfer of part of the energy from capacitor 31 to capacitor 36.Capacitor 31 commences to recharge once more and again reaches thereference line r at which point Shockley diode 32 breaks down andtransfer a further charge to capacitor 36. Capacitor 31 again commencesto recharge but before it reaches the reference line waveform 1 goesnegative causing transistor 18 to become non-conductive and transistor26 to become conductive. This cycle is repeated when waveform once moregoes in the positive direction.

The waveform at j shows the periods of conductivity of transistor 39-or49 since both obey substantially the same law. Waveform j isparticularly referred to waveform h and as will be seen transistor 39remains nonconductive until waveform it reaches the reference line r, atwhich point the charge transferred to capacitor 36 causes transistor 39to become conductive. The Charge on capacitor 36 maintains thetransistor 39 conductive until capacitor 36 is sufficiently dischargedthrough resistors 37 and 38 to permit the base of transistor 39 toapproach the potential of the negative bus 21. This same event occurs inthe second waveform. In the third waveform, however, it will be notedthat two charges are transferred from the capacitor 31 to capacitor 36and the discharge does not begin to occur until after the end of thesecond transfer. After this point the capacitor 36 gradually dischargesand transistor 39 eventually becomes non-conductive and does not conductagain until a further charge is transferred from capacitor 31 tocapacitor 36 in response to breakdown of the Shockley diode 32.

When the value of resistor 28 is still further reduced the rate ofcharge of capacitor 31 is increased and the number of chargestransferred from 31 to 36 is increased and as shown in the latterwaveforms the capacitor 36 does not begin to discharge until the lastcharge is transferred and therefore transistor 39 remains conductive themajority of the time with only a slight period occurring when transistor39 is not conducting. Waveform k is similar to waveform 1' but withparticular reference to waveform 1'. It will be seen that theconductivity of transistor 39 remains a minimum until the third waveformof waveform i, at which point the Waveform for the first time touchesthe reference line r causing a transfer of energy from capacitor 31 tocapacitor 36. Energy as before causes the base of transistor 39 to gopositive and remain positive until the charge is dissipated throughresistors 37 and 38. Transistor 39 therefore remains conductive for alimited period of time and once more becomes conductive when again thewaveform i touches the reference line r. When the resistor 28 is reducedstill further the waveform i reaches the reference line sooner,transistor 39 becomes conductive at a point earlier in time and remainsconductive for a greater proportion of the cycle as is shown in thelatter two cycles of Waveform k.

From all the foregoing it will be apparent that by selection of thevarious resistors and capacitors the transistor 39 may be maintainedconductive for various portions of the cycle depending upon the waveformapplied to the base of transistor 18 and in turn relay 40 may be madeoperative depending upon its own characteristic and held in dependingupon the normal delays inherent in the relay, in response to any givenWaveform input to transistor 18. By adjustment of resistor 28 the effectof an input waveform to transistor 18 may be adjusted so that the relaymay be caused to hold or drop out in response to a particular waveformapplied to the base of transistor 18 which is equivalent to saying thatthe relay may hold in or drop out in response to a particular phaserelationship between the signals applied to the ring modulator. As willbe seen from waveforms j and k a circuit arranged so that the relay 40will just hold in response to waveforms of the type shown in the firsttwo cycles of waveform j and the last two cycles of waveform k and willremain held in response to the other forms of cycles shown in the latterpart of waveform j but will drop out for the waveforms shown in theearlier portion of waveform k. The waveforms shown at j and k will alsoappear in inverted form at terminal 54 and may be used to control somefurther apparatus or create some'further indication of condition ofrelay.

The time required for capacitor 31 to be charged to the breakdownpotential of Shockley diode 32, is of course a function of thepotentials applied to resistor adjustor 28. This time may be calledalpha and expressed as electrical degrees wherein a 60 cycle system, 360is equivalent to 16.66 milliseconds. Bearing this in mind andconsidering FIG. 4, the diagram at A in FIG. 4 illustrates the situationwhere alpha is adjusted to The vertical vector represents 3V or the zerosequence voltage. The

relay has been designed to operate with a maximum duration of pulsesapplied to the base of transistor 18 when the applied current lags thevoltage by 90. Therefore the vector in a horizontal direction pointingin the right represents 31 for a maximum pulse duration applied to thebase of the transistor 18. Under these circumstances the relay willoperate if the current vector falls anywhere within plus or minus 90 ofthe minus 3I 'line or the horizontal vector. By different adjustment ofresistor 28, alpha may be made equal to that is the charging time willbe approximately 5.555 milliseconds and the relay will operate if thecurrent lies within plus or minus 60 of the horizontal vector. As shownat C in FIG. 4, alpha may alternatively be adjusted to 60 and underthese circumstances the relay will operate if less than current vectorlies within plus or minus 120 of the horizontal vector. As will beapparent, various adjustments of the value alpha may be made to adaptthe relay to the particular application.

FIGS. 3A, 3B, 3C and 3D illustrate the various arrangements forutilizing this relay for different functions. Considering FIG. 3A first,this illustrates the necessary circuit arrangement for utilization ofthis relay as a ground directional relay with potential polarization andzero sequence current compensation. As will be seen, power is suppliedfrom three phases a, b and c to the primary of a three phase transformer61 with the primary connected in delta. The secondary of the transformeris connected in star and the star point connected to ground. The outputfrom the secondary of this transformeris connected to a load throughcircuit breaker 62. The potentials on the various phases on thesecondary of trans former 61 are combined potential transformers 63, 64and 65 which are connected in star across the phases a, .b and 0respectively, with their star points connected to ground. Theirsecondaries are connected in series to terminal 1. The currents to theload are derived by current transformers 66, 67 and 68 and the zerosequence derived by joining the terminals of the current transformerstogether at the star point D which is grounded and at the point A.Correspondingly designated terminals are connected together between FIG.3A and FIG. 1.

As will be seen the first voltage applied to the ring modulator isapplied to terminal 1 and polarizes the relay by providing a referencevoltage. The zero sequence current derived from the current transformerspasses through, the primary of mutual inductor 4 from terminal A toterminal B. Terminal B is connected to terminal C and the same currentpasses through the primary of mutual inductor 12, to terminal D. Theoutput from the secondary of mutual inductor 12 provides the secondinput to the ring modulator and the zero sequence current therefore iscompared in phase with the reference voltage. At the same time a voltageproportional to the zero sequence current is applied in series with thereference voltage to compensate for the insensitivity which would becaused by low source impedance and low fault current.

FIG. 3B illustrates the arrangement for providing both voltage andcurrent polarization. As before, three buses a, b and 0 provide thecurrent to transformer 61 and the secondary of this transformer isconnected in star with its star point grounded. The current from thestar point to ground, however, is passed through a current transformer69 and the output of this current transformer applied to terminals A andB. The voltage for polarization is derived as before from the potentialsof the three phases through potential transformers 63, 64 and 65 and thezero sequence current flows from terminal C to terminal D to ground. Theoperation is similar to the operation described for FIG. A and the phaseof the zero sequence current is compared with the phase of the combinedeffect of the potential provided to the ring modulator from. thepotential transformers 63, 64 and 65 and the current applied in seriesfrom the current transformer 69.

FIG. 30 illustrates an arrangement similar to the preceding arrangementswhere only current polarization is provided. The current from thecurrent transformer 69 is applied to terminals A and B and the zerosequence current from terminal C to ground is applied to terminals C andD, and the phase relationship of those two currents is measured.

FIG; 3D illustrates the circuit arrangement for operation of a group ofthree of these relays for distance relaying. As before, the three busesaredesignated a, b and c and are supplied through a circuit breaker 62and the current from the circuit breaker to the load passes throughcurrent transformers 66, 67 and 68. In order for a suitable signal to beprovided through the relays, it is necessary to combine several factors,for example, one relay must respond to the potential between buses a, band c. To this end a potential transformer is provided designated 70which is connected to the three phases and a voltage is derived from thesecondary of this transformer such that the potential between buses aand b corresponds to the potential between terminals designated 1a and1b. This potential may be applied to terminals 1 and D of the relay toprovide the voltage polarization or reference voltage for the ringmodulator. The other signal to be provided is a function not only of thepotential between phases a and b, but also the current in phase a andthe current in phase b. To this end, mutual reactors 71, 72 and 73 areprovided and mutual reactor 71 provides a signal representative of thecurrent from current transformer 66 which is introduced into one primaryof the mutual reactor 71 and also the current in phase b from currenttransformer -67 which is introduced into the second primary of mutualreactor 71 in a subtractive manner so that the output from mutualreactor 71 in its secondary represents the current in phase a minus thecurrent in phase b. In a similar manner the output from mutual reactor72 is a function of the current in phase b minus the current in phase cand the output from mutual reactor 73 is a function of the current inphase minus the current in phase a. The potential across terminals C andD therefore may be expressed as the potential between phase a and phaseb minus the current dilference between these two phases times somefunction.

Between the secondary of mutual reactor 71 and terminal C there isintroduced a filter designated 75 which shall be referred to as aswitched filter circuit. Similar devices 76 and 77 are introducedbetween the secondaries of mutual reactor 72 and terminal C and thesecondary of mutual reactor 73 and terminal C The operation of theseelements will be described in conjunction with FIGS. 5 and 6, butgenerally it may be assumed that these devices operate to select thedesired operating frequency and reject transients but are operative onlyunder certain circumstances.

If terminal C is now connected to terminal C of FIG. 1 and terminal D,is connected to terminal D of FIG. 1 and terminal 1 is connected toterminal 1 of FIG. 1, then relay is provided with suitable signals fordistance relaying. In order to combine the output from three suchrelays, that is one for each phase, it is possible to utilize a separatering modulator for each phase and separate charging circuits and thencombine the outputs at a later point in the circuit. To this end, thecircuits may be open between points E and F in FIG. 1 and terminal F ofFIG. 3D connected to terminal F in FIG. 1, and

the E terminal of the a relay connected to terminal E in FIG. 3D. In asimilar manner the E terminal of the b relay will be connected to E, ofFIG. 3D and the E terminal of the c relay will be connected to E of FIG.3D. The common la-tter portion of the relay, that is the elements afterterminal F may then be used as a common output for all three phases andthe output from terminal 60 of this combined relay may be applied toterminal 60 of FIG. 3D to control the circuit breaker 62.

When operating in this mode the secondary mutual reactor 12 andcapacitor 13 do not combine to produce a resonant circuit because such aresonant circuit would produce undesirable delays. In fact capacitor 13may be omitted. The selective function performed by this tuned circuitin previous modes of operation is performed in this circumstance byswitched filters 75, 76 and 77 which are more completely described inassociation with FIGS. 5 and 6. In order to better appreciate theproblem, it should first be considered what the signal across terminals(3,, and D presents. In fact it is the voltage across phases A and Bminus a function times the difference between the currents in phases Aand B. Under normal operating conditions the latter part of thisfunction will be essentially zero and the voltage across phases A and Bwill be a constant therefore if this signal is applied to a filter, thefilter will be energized and will have stored a certain amount ofenergy. If now a fault occurs, the factor proportional to the differencebetween the current and phase A and current in phase B must reverse indirection and the amount of energy available in this reverse directiondepends upon the magnitude of the fault current and the fault location.It will therefore be apparent in order that the relay may detect smallfault currents or distant faults, the potential across terminals C and Dmust be enabled to change rapidly and it must not be necessary to firstdissipate the energy of the filter. To this end the filters 75, 76 and77 are switched and are operative only after a fault occurs. Means ofobtaining this end is shown in FIGS. 5 and 6.

Considering first FIG. 5 there will be seen three terminals which areindicated as being connected to phases a, b and c. The a terminal isconnected through capacitor 78 and inductor 79 and a double anode Zener80 to one end of the primary transformer 81. Phases b and c areconnected to centre tapped reactor 82. Phase c is also connected throughresistor 83 to the junction of reactor 79 and Zener 80'. The centre tapof the reactor 82 is connected to the remaining terminal at the primaryof transformer 81. Primary 81 has three secondaries, one for each phaseto be controlled. Those not actually being described are shown in dottedlines. The secondary actually being used in the circuit is connected toa bridge rectifier 84 and the DC output from this bridge is applied tocapacitor 85 and through reactor 86 to the base of transistor 87. Fourdiodes 88, 89, and 91 are arranged in a bridge. The anodes of diodes 88and 89 are connected together and are connected to the collector oftransistor -87. The cathodes of diodes 90 and 91 are connected togetherand connected to the'conductor 92 which is also connected to the emitterof transistor 87 and the negative terminal of rectifier bridge 84. Aseries tuned filter comprising inductor 93 and capacitor 94 andincluding two resistors 95 and 96 is connected between terminals 75a and75b. It will be understood that terminals 75a and 75b represent theterminals of filter 75 in FIG. 3D. Components 93, 94 and 95 are chosento provide the desired filter effect whereas resistor 96 is suflicientto lower the Q of the resonant circuit to such a degree that very littleenergy is stored in the filter. The operation of this circuit may beexplained as follows.

With a fault on the system, negative sequence current flows causing acurrent from phase a to flow through the primary of transformer 81 tothe center tap of reactor 82. The components are so chosen that when anormal positive sequence voltage is applied to terminals a, b and cthere is no input to transformer 81. However, when negative sequencecurrent occurs due to a fault there is an input to transformer 81.Because transients may under some circumstances not be present,capacitor 78 and conductor 79 are included to ensure that there arereactive components present at all times to energize transformer 81. Thedouble anode Zener 80 limits the signal applied to the transformer 81.The output from the transformer is applied through bridge 84 tocapacitor 85 which stores the output together with reactor 86 to ensurethat once a signal is produced it remains on the base of transistor 87for an appreciable length of time, for example, something in the orderof 100 milliseconds. As long as transistor 87 is conductive, terminals Gand H are in effect shorted together thus eliminating resistor 96 fromthe circuit. Under these circumstances the filter is effective and iftuned to resonate at the network frequency eliminates transients. Sinceas was previously indicated the filter is effective only during a fault,no energy is stored previous to the commencement of the fault. In thisway the advantages of filtering are obtained without the concurrentdisadvantage of delays caused by energy storage within the filter. FIG.6 shows an alternative arrangement including resistors 97 and 98 and aparallel tuned filter comprising inductor 99 and capacitor 100.Terminals G and H from the previous circuit, that is from the bridgecomprising diodes 88 to 91 are connected in series with the paralleltuned circuit. With terminals G and H open circuited, the tuned circuitwhich is resonated at the system frequency is not operative andtherefore no energy is stored in it. However, when a fault occurs andterminals G and H are short circuited, the paral el tuned circuitbecomes effective responding selectively to the normal system frequencyand eliminating transients from the signal. As before, the terminals ofthis filter are designated 75A and 75B and represent the terminals offilter 75 in FIG. 3D.

All of the advantages previously noted with reference to this relay areequally applicable to these applications and it will be noted forexample with reference to FIG. 3D that the output from terminal 1 isapplied to the primary of mutual reactor 3 and as before this is a tunedresonant circuit which responds with greater sensitivity to signals ofthe supply frequency than to signals of the supply frequency than tosignals of other frequency and the comomn output described inassociation with FIG. 3D minimizes the number of elements required toperform the desired function.

It will be appreciated that the relay as described may also beapplicable in other situations and that various substitutions may bemade for various elements as described in FIG. could be replaced by amechanical switch provided the mechanical switch had a sufiiciently highoperating speed. Even in this case, however, it would seem advisable toutilitze the negative sequence current as the actuating signal forcontrolling relay.

As was previously indicated, FIG. 7 at A, B and C illustrates threepossible RX characteristics obtainable by varying alpha the time settingof the relay. When alpha is adjusted to 90 the conventional mhocharacteristic is obtained. The line OZ represents the relay setting andsubtends an angle at the circumference of the characteristic equal tothe angle alpha. With alpha adjusted to 120 as illustrated at B of FIG.7 the operating characteristic is restricted which limits theprobability of the relay operating on power swings and may beparticularly useful on long lines. At C there is illustrated acharacteristic where alpha is less than 90, for example, and theoperating characteristic is enlarged. Such a characteristic, from itsgreater tolerance to fault resistance, has particular utility on shortlines. It will be evident that other intermediate values may be utilizedwhere advantageous.

What is claimed and is desired to be secured by United States LettersPatent is as follows:

1. In a fault sensing relay for an alternating potential electric powertransmission line, a phase discriminator having first and second inputsand an output, supply means effective to supply first and secondelectrical quantities individually to said first and second inputsrespectively, the phase angle of one of said quantities being dependentupon the operating condition of said line, a tuned filter connectedbetween said supply means and the one of said inputs to which said onequantity is supplied, said filter including a Q controlling element, andQ controlling means operatively connected to said Q controlling element,said Q controlling means normally being effective to maintain a reducedQ in said filter so that a reduced storage of energy is maintainedtherein and the filter has a low time interval of response to a changein the phase of said one quantity, said Q controlling means beingactuatable in response to a fault condititon of said transmission lineto raise the Q of said filter to increase its filtering ability.

2. The combination of claim 1 in which said one quantity isrepresentative of current flow in said line and the other of saidquantities is representative of a voltage condition of said line.

3. The combination of claim 2 in which said transmission line ispolyphase and said Q controlling means is responsive to the presence ofnegative sequence current in said polyphase line.

4. The combination of claim 3- in which a second filter, tuned to thefrequency of said transmission line, is connected to the input of said Qcontrolling means to reduce the effect of transient quantities.

References Cited UNITED STATES PATENTS 2,922,109 1/1960 Hodges et al.31736 X 3,210,606 10/1965 Calhoun 317-36 3,214,641 10/1965 Sonnemann31733 3,353,081 11/1967 Stemmler 3216 JAMES D. TRAMMELL, PrimaryExaminer US. Cl. X.R.

